NWS Forecaster Discussion

Area forecast discussion
National Weather Service Greenville-Spartanburg SC
435 PM EST Tuesday Mar 3 2015
Synopsis...
moist and milder air will return to the area Wednesday ahead of an
approaching cold front. This front is forecast to pass through the
area on Thursday...with cool and dry high pressure returning for
Friday and into the weekend.
&&
Near term /through Wednesday/...
as of 430 PM...no major changes were needed to the going forecast. Isen
charts at 285k indicate cpd/S will remain very low while The
Wedge continues to break down...so low clouds and areas of very
light rain and patchy dz will persist through the next update.
Aligned probability of precipitation close to cam probability of precipitation with the better coverage remaining
over the SW/rn zones in mech lift.
As of 1230 PM...patches of light rain and drizzle continue to move
east mainly across NE Georgia and upstate SC...and the southern part of
the clt metropolitan area. This was in general agreement with some of the
mesoscale models. The light precipitation and cloud cover has kept temperatures
cool and in line with previous thinking. No significant changes will
be made.
For tonight...a slowly evolving upper pattern with the axis of an
upper ridge moving off the East Coast will carry surface high pressure
away and further offshore...thus removing any connection between the
parent high and our weak hybrid wedge. At the same time...moist
isentropic low level upglide will shift to the NE...carrying most of
the leftover light rain with it. That will leave most of the
Piedmont mainly dry overnight with winds coming around to the southeast or
S to move out the remnants of the low level cool pool. As this
happens...cannot rule out a period of patchy dense fog as warm
advection begins near the surface. The warm advection should result
in temperatures rising gradually overnight. A chance of precipitation will
be retained over the mountains and foothills where some small upslope
component will continue. Fortunately...temperatures will remain above
freezing so no p-type problems are expected.
On Wednesday...the models show a classic anafront approaching slowly
from the west as it fights its way against the west-southwest flow aloft.
Forcing east of the mountains will be minimal...other than the low level
warm advection...which supports keeping a pop gradient up against
the higher terrain. The precipitation probability ramps back up to likely
in the morning and then categorical in the late afternoon along the
Tennessee border as the front moves in. Some low mu cape suggests there
could be some embedded thunderstorms along the front. Temperatures ahead of
the front will bounce back 20 to 25 degrees above tuesdays highs...
continuing our recent roller coaster stretch of high temperatures.
&&
Short term /Wednesday night through Friday/...
at 230 PM EST Tuesday...the short term period initializes on
Wednesday evening amidst flat upper ridging aloft over the
southeast while a short wave trough digs across the northern plains.
At the surface...warm air advection regime prevails across the southeast ahead of
an approaching cold front. The forecast initializes with likely probability of precipitation
across the high terrain as the primary moisture/frontal axis slides
through the Tennessee Valley...with some upslope enhancement
possible. Probability of precipitation decrease further east with no mentionable probability of precipitation at
initialization along and south of Interstate 85. Probability of precipitation will
gradually ramp up through the overnight into the Thursday morning as
the front intrudes from the west...with widespread likely level
probability of precipitation featured by midday.
Models continue to hint at weak instability ahead of the frontal passage in
the warm sector...which could promote a few rumbles of thunder
across portions of northeast Georgia...and the western Carolinas early on
Thursday. Otherwise...as cold advection prevails behind the
front...expecting a fairly quick transition of ptype along the Tennessee
line before all precipitation exits the region into the late afternoon
hours. Expecting phases changes from rain to a brief period of
freezing rain before sleet then finally snow...all within 6-8
hours. Not expecting any accumulations to exceed advisory levels.
Beyond that...the front will slide east through Thursday evening
with all probability of precipitation removed from the forecast not later than midnight. High pressure
will quickly slide in behind the front across the Ohio Valley before
setting up a brief cad wedge regime for early Friday.
Thus...expecting Friday to be dry...with cloudy skies early on
before weak wedge quickly retreats and sunny skies prevail by the
afternoon hours. Temperatures through the period will feature near
normal levels on Thursday before falling to well below normal for
Friday.
&&
Long term /Friday night through Tuesday/...
as of 200 PM Tuesday...high pressure will remain in control over the
Carolinas and vicinity Friday night through Monday. A shallow eastern Continental U.S. Trough
will still be present aloft...and the the northern stream will remain
somewhat active. A weak cold front will sweep through Sat night or sun
but with very little moisture...albeit enough to mention some upslope
probability of precipitation along the tenn border. The front will basically allow a
transition from one surface high to another...though little to no change
in temperatures is expected. Thicknesses increase gradually over the course
of the period and min/maximum temperatures will be near climatology by Sunday. The
second area of high pressure will move offshore early-middle next week
as split flow develops in the southern stream...leading to the development
of a wave along the stalled boundary over the northern Gulf of Mexico.
Global models differ on the timing of this feature...but eventually
said wave could spread warm frontal precipitation into the County warning forecast area. 03/00z and
12z ec both do so by Monday night...but the 03/12z GFS delays it
until well beyond the end of the forecast period. Low probability of precipitation will return
across the County warning forecast area in a nod to the ec solution. Surface temperatures will dip below
freezing over much of the higher terrain Monday night. In light of the
strong warm nose that would be expected...some light freezing rain may occur
there.
&&
Aviation /22z Tuesday through Sunday/...
at kclt...a difficult situation for the afternoon...as some
variability is expected with wind direction alternating back and
forth between east-northeast and east-southeast. The trend should be toward the wind
veering around to southeast later today. The ceiling and visibility will
also be variable between IFR/MVFR until early this evening...when
the model guidance suggests we will lock in the low IFR for the
overnight period. A light wind coming around to southeast will only help
with some weak moist upglide. At the same time...the flow at 850 mb
will strengthen as the core of a low level jet translates east across
the region...which should result in some low level wind shear
developing the pre-dawn hours. Some improvement is expected in the
middle to late morning with boundary layer warming and a reduced threat
of light precipitation.
Elsewhere...similar to kclt. The NE wind may hold on the longest at
khky...but most places outside the mountains will keep a prevailing NE
wind until some time in the early evening...around 02z...when wind
will probably go light and variable. Guidance is quite pessimistic
with IFR/LIFR conditions indicated.
Outlook...a cold front will move slowly through the region Wednesday
through Thursday...bringing chances for heavier rainfall and low
ceilings/visibilities to the area. VFR conditions are expected to return for
Friday and Saturday.
Confidence table...
13-19z 19-01z 01-07z 07-12z
kclt high 95% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl medium 74% high 100% high 100% high 100%
khky medium 77% high 100% high 100% high 100%
kgmu high 100% high 100% high 100% high 100%
kand high 100% high 100% high 100% high 100%
The percentage reflects the number of guidance members agreeing
with the scheduled taf issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link: (must be lower case)
Www.Weather.Gov/gsp/aviation_tables
&&
Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.
&&
$$
Synopsis...Wimberley
near term...PM/sbk
short term...cdg
long term...Wimberley
aviation...PM